This invention relates generally to bending metal pipe and more particularly, relates to bending relatively thin-walled corrugated metal pipe to selective angles along its length which enables its special application to automotive exhaust systems.
Heretofore, metal pipe has been bent mainly by a method employing so-called "brute force". The pipe is inserted between an arcuate, convex radius die and a pair of pivotally mounted and spaced apart back shoes. A hydraulic ram moves the radius die perpendicular to a line between the back shoes and against the pipe which, in turn, engages against the pair of back shoes. The radius die then is advanced to bend the pipe. The distance that the radius die is advanced or the depth of the bend then becomes the bend angle formed in the pipe. The radius of the bend is determined by the radius of arc of the die.
This "brute force" method functions by stretching the pipe wall material at the heel or outer radius of the bend and by compressing the wall material of the pipe at the throat or inner radius. Forming small radius bends in thick-walled, small diameter pipe in this manner presents a few problems. There is sufficient material in the pipe wall to provide for the stretching of the heel material while maintaining the pipe cross-sectional geometry. Essentially, the stretched pipe wall retains enough strength to maintain its configuration and not collapse or significantly deform. The throat material is strong enough not to buckle. Such is not the case, however, in bending thin-walled, large diameter pipe.
Thin-walled pipe is commonly referred to in the automotive industry as tubing and corresponds to pipe having a wall thickness of approximately 0.083 to 0.036 inch. Although presently this is the range commonly found for automotive-type pipe, it is contemplated that pipe wall thicknesses may be reduced even further to perhaps 0.012 to 0.014 inch using stainless steel material.
With so-called thin-walled, large diameter pipe, the pipe may have sufficient strength to maintain its configuration during the forming of large radius bends. However, for small radius bends, the thickness of the heel wall material is reduced due to the stretching beyond the point at which the pipe wall has the necessary strength to retain its shape. The heel of the pipe then collapses or flattens sufficiently to reduce the interior diameter of the pipe. The wall of the pipe at the throat may also distort, which may result in a resistance to the bending in the form of buckling of material thereat.
Substances such as sand or implements such as arbors have been known to be inserted on the interior of so-called thin-walled pipe prior to the bending operation so as to assist in maintaining the cross-sectional shape during formation of a small radius bend. However, these aids are not always feasible or usable, especially where multiple bends or reverse bends must be formed in the pipe.
Indeed, a need exists generally to be able to bend such thin-walled, large diameter pipe free from these problems. Further, in both O.E.M. automotive exhaust systems and after market replacements thereof, the need is acute because specially bent pipe configurations are required to be used or, in the after market replacement area, special configured out of stock or non-stock items must be provided quickly. Several different machines are commercially available which bend smooth-walled pipe by the described brute force method. These commercially available machines do not solve the problems described hereinabove.
Corrugated pipe has a structure that consists of annular ridges and valleys, the valleys being located between the ridges along the length of the pipe and may be likened to gussets. In a straight or unbent section of pipe, the ridges have their axes parallel to one another and perpendicular to the longitudinal axis of the pipe. The valleys represent the basic pipe diameter and the ridges represent the expanded outer diameter of the pipe. This results in development of a modulus of section that enables the thin-walled pipe to have rigidity and strength sufficient to maintain its configuration as well as to be bent to multiple angles required for application to automotive exhaust systems. Heretofore, the normal gauge for such corrugated pipe was approximately 20 gauge or 0.036 inch thick. It was contemplated that bending of such reduced wall thickness pipe in conjunction with corrugated configuration would facilitate such bending requirements. In practice, however, this advantage was not realized.
Such thin-walled, corrugated pipe has been used previously in the after market product field for exhaust and tail pipes. This thin walled, corrugated pipe heretofore has been bent in the conventional manner but for bending purposes, its thinner walls tend to aggravate the problems described hereinabove.
This invention provides a novel method and an apparatus for incrementally bending thin-walled corrugated pipe. Essentially, the configuration of the pipe wall at the valleys is reformed by bending, not stretching or compressing, to provide the desired bend angle. The desired bend angle of the pipe is achieved by incrementally deforming the pipe in one or more adjacent valleys. Forming a bend in such corrugated pipe by control bending of the gusset material at the valleys eliminates the undesired stretching and/or compressing of material where the brute force method was employed.
When such corrugated pipe is bent, the normal parallel relationship of the ridges is changed so that in the vicinity of the desired bend, the axes of the ridges are non-parallel one with respect to the other, but still perpendicular to the longitudinal axis of the pipe. Here, the linear distance between adjacent ridges at the heel of the bend is increased and the corresponding linear distance at the throat of the bend is decreased, resulting in a segmental arc or incremental bend.